In portable devices, touchscreens serving as both display devices and input devices have been extensively used since before. As input interfaces employing touchscreens, fixed button-based user interfaces, shown in FIG. 9, and position-independent user interfaces, shown in FIG. 10, exist.
In fixed button-based user interfaces, as shown in FIG. 9, various specific indications 501 to 510, including a button and a cross key for input and other elements related to input events, are displayed in a superimposed manner on a main image (an image of a person and scene). Furthermore, input events are detected only in cases where a player's finger touches limited places, such as the specific indication 501 representing a button and the specific indication 502 representing a cross key.
On the other hand, in position-independent user interfaces, as shown in FIG. 10, the specific indications 501 to 510 do not exist, and input events are detected when a player's finger 601 touches arbitrary positions on the screen (touchscreen), while a main image (an image of a person and scene) is displayed without being hidden.
Compared with fixed button-based user interfaces, with which it is necessary to constantly display buttons and a cross key on the screen, position-independent user interfaces, with which touch operations are allowed at arbitrary positions on the screen (touchscreen), are particularly effective when playing games on portable terminals such as smartphones, for which the screen sizes are limited.
However, in games employing position-independent user interfaces, it is not possible to uniquely determine an action from a single touch operation by a user. For example, at the moment when a user touches a part of a screen, it is difficult to uniquely determine whether the touch is a single tap operation for selecting an item or character displayed at that position, the start of successive tap operations on the screen, or the start of a swipe operation for designating a direction. Thus, in order to enable unique determination of all operations, it has been the case with conventional position-independent user interfaces to adopt a method in which the possible kinds of user inputs are considerably limited, a method in which areas that can be tapped are broadly segmented, a method in which what is input is fed back on the screen in real time so that the user can immediately recognize incorrect inputs, and so on (e.g., see Patent Literature 1).
Furthermore, in position-independent user interfaces in fields other than games, gesture input is well known. For example, Patent Literature 2 discloses a user interface having a function for recognizing gestures made by combining graphics such as circles and rectangles, symbols such as check marks and question marks, and characters such as letters of the alphabet and a function for allowing users to individually customize gestures.
Patent Literature 1: Japanese Unexamined Patent Application, Publication No. 2011-076588
Patent Literature 2: Specification of U.S. Pat. No. 8,379,098